Hunchentoot
Hunchentoot is a robust and easy to use HTTP server. As a stand-alone web server, Hunchentoot is capable of HTTP/1.1 chunking (both directions), persistent connections (keep-alive), and SSL, but it can also sit behind the popular Apache using Marc Battyani's mod_lisp.

Since 2015, the community advices not to use Hunchentoot directly but to use Clack or a webserver built on top of it, like Caveman, Ningle or Lucern.

Hunchentoot currently works with LispWorks (which is the main development and testing platform), CMUCL (with MP support), SBCL (with Unicode and thread support), OpenMCL, and ACL.

It's written by Edi Weitz and can be found at http://weitz.de/hunchentoot/.

Cyrus Harmon has contributed support for virtual hosts, CGI, and authentication in Hunchentoot.

2011: Hunchentoot has moved to github at https://github.com/edicl/hunchentoot/downloads